The present invention relates to a swing-type actuator such as an actuator for magnetic disk drives, and more particularly to an improved thin swing-type actuator capable of swinging a function member such as a magnetic head along a circular course.
Conventionally, the positioning of a magnetic head on a recording track of a magnetic disk, etc. is conducted by a swing-type or rotation-type actuator as shown in FIGS. 19(a) and (b). In both figures, one yoke 1b is fixedly provided with permanent magnets 3, 3, and a pair of yokes 1a, 1b are assembled by supports 2, 2 such that different magnetic poles of the permanent magnets 3, 3 are opposing a magnetic gap 4 to form a magnetic circuit. An arm 5 has an aperture 7 in a center portion. A shaft (not shown) is rotatably fitted in the aperture 7, so that the arm 5 is rotatably supported by a housing (not shown). The arm 5 is also provided with an aperture (not shown) at one end for mounting a function member (not shown) such as a magnetic head to the arm 5. The arm 5 is arranged such that the movable coil 6 located in the magnetic gap 4 can swing around a shaft 7.
When an operation signal is supplied to the movable coil 6, a magnetic force generated from the movable coil 6 according to Fleming's left hand rule functions as an attraction force or a repulsion force to each permanent magnet 3, so that the arm 5 is rotated around the shaft inserted into the hole 7. As a result, a magnetic head fixed to a tip end of the arm 5 is positioned on a desired magnetic track of a magnetic disk (not shown). The direction of the rotation of the arm 5 can be changed by inverting the direction of current applied to the movable coil 6.
FIG. 20 is a perspective view showing members constituting the magnetic circuit of FIG. 19, and FIG. 21 is an exploded view showing them. In these figures, the same reference numerals are assigned to the same members as in FIG. 19. To regulate the swing span of the movable coil 6, there are stoppers 8, 8 mounted to the lower yoke lb. Positioning pins 9, 9 . . . are mounted to the lower yoke 1b to fix a permanent magnet 3 at a desired position by contact with a periphery of the permanent magnet 3.
In the assembling of the members shown in FIG. 21, the positioning pins 9, 9 . . . are first mounted to the lower yoke 1b at desired positions, and the permanent magnet 3 is then fixed to the lower yoke 1b by an adhesive. In this case, to cure the adhesive, it is necessary to heat and dry it, requiring a lengthy and troublesome operation of bonding the permanent magnet 3 to the lower yoke 1b. This leads to a large cost for the production of the swing-type actuator. Also, when the swing-type actuator is heated to dry and cure the adhesive, a harmful gas is generated from the adhesive, causing an environmental problem.
Next, after the permanent magnet 3 is fixed to the lower yoke 1b, supports 2, 2 and stoppers 8 are fixed to the lower yoke 1b, and then the upper yoke 1a is fixed to the supports 2, 2 by screws 2a, 2a. Since these members are fixed by screws and/or press-fitting, manual labor is needed extensively. Therefore, the production of the conventional swing-type actuator is costly because of long working time and many steps.
Recently, demand has become increasingly higher to make such a swing-type actuator thinner and less expensive. However, the above conventional swing-type actuator fails to meet such a demand because it is constituted by many parts and assembling of parts takes long working time.